1. Field of the Invention
The present invention relates to an ophthalmic laser treatment apparatus arranged to irradiate a laser beam to a patient's eye for treatment.
2. Description of Related Art
An ophthalmic laser treatment apparatus arranged to irradiate a laser beam to a patient's eye includes a laser source which emits a treatment laser beam, an optical fiber for transmitting the laser beam from the laser source, and a delivery optical system provided with a variable power optical system for focusing the laser beam transmitted through the optical fiber at a spot size adequate for treatment purposes. An optical fiber used in a photocoagulation treatment laser apparatus is usually a multimode fiber having a core diameter of about 50 μm. Further, a delivery unit is provided with a variable zoom optical system for changing the laser spot irradiated on the fundus in a range of 50 μm to 500 μm. In laser iridotomy, the magnification of the variable zoom optical system is set at about 50 μm which is a minimum magnification so that energy density is increased in use.
Meanwhile, the multimode fiber is apt to generate a speckle pattern in a beam profile at a fiber emission end face. This may cause uneven burning in the fundus photocoagulation treatment, and hence a uniform coagulation spot could not be formed. In this regard, there have been proposed a technique of preventing the generation of a speckle pattern (refer to for example U.S. Pat. No. 7,082,151 (JP2004-135971A), US2005027288A1 (JP2005-46247), and JP2003-310653A) and a technique of changing an intensity distribution of a spot on an affected part (refer to for example JP2001-8945A, U.S. Pat. No. 7,044,943 (JP2004-229965A)).
The above proposed techniques have disadvantages such as a decrease in fiber transmittance, and a difficulty in placing and adjusting a mechanism for oscillating the multimode fiber. It is therefore desired to efficiently improve a beam quality by a simple structure. Further, in the case of using a single mode fiber instead of the multimode fiber, a beam profile at an emission end face of the single mode fiber is Gaussian, which would cause excessive coagulation in a center area of an irradiated part of an affected part. Furthermore, when a spot size of 50 μm to 500 μm is to be obtained on the fundus by use of a single mode fiber having a core diameter of about 5 μm, a variable power optical system capable of providing higher magnification is required. Such an optical system is difficult to manufacture. In the case where the aforementioned fiber is not used for transmission of a laser beam, for example, even in an apparatus including a laser source integral with a delivery optical system, a beam profile of the laser beam emitted from the laser source is Gaussian.